Gelatin-modified polyurethane and polyester film base

ABSTRACT

The present invention is an imaging base which includes a polyester film support and an adhesion promoting layer directly adhered to a surface of the support. The adhesion promoting layer is formed by the coating and subsequent drying of a coating composition comprising a gelatin-grafted-polyurethane. The gelatin-grafted polyurethane is covalently bound to the polyurethane through a grafting agent wherein the ratio of gelatin to polyurethane is from 1:10 to 2:1. In one embodiment of the invention the imaging support is coated with at least one silver halide emulsion layer to form a photographic element.

CROSS REFERENCE TO RELATED APPLICATIONS

This application relates to commonly assigned copending application Ser.No. 09/090,831, Docket 77,907) filed simultaneously. This applicationrelates to commonly assigned copending application Ser. No. 09/090,579,filed simultaneously herewith. This application relates to commonlyassigned copending application Ser. No. 09/090,578, filed simultaneouslyherewith. This application relates to commonly assigned copendingapplication Ser. No. 09/090,827, filed simultaneously herewith.

FIELD OF THE INVENTION

The present invention relates to water-dispersible polyurethanes and tothe use of such materials in photographic materials. In particular theinvention relates to water-dispersible polyurethanes that have beengrafted to gelatin and the use of these compositions in adhesionpromoting layers for polyester film base.

BACKGROUND OF THE INVENTION

It is difficult to adhere photographic emulsions to oriented polyestersupports, such as polyethylene terephthalate and polyethylenenaphthalate. This problem is exacerbated by the conditions to whichphotographic elements are subjected; i.e., the adhesion must not fail inthe raw and processed dry state, as well as when the film is wet duringthe development process.

Several adhesion promoting "subbing" materials, such as poly(methylacrylate-co-vinylidene chloride-co-itaconic acid) andpoly(acrylonitrile-co-vinylidene chloride-co-acrylic acid) disclosed inU.S. Pat. Nos. 3,201,249 and 3,143,421, respectively, provide therequired adhesion when applied before orientation but are not aseffective when applied on oriented support. The effectiveness of theseadhesive materials may be enhanced by the use of swelling or attackagents such as resorcinol.

An alternative approach disclosed in U.S. Pat. No. 4,695,532 describes adischarged treated polyester film support having coated directly thereona crosslinked layer of an aqueous vinyl acrylate copolymer and gelatinmixture. Although this system has good adhesion before processing, theadhesion performance is severely degraded by photographic developingsolutions.

U.S. Pat. No. 5,639,589 discloses a polyester film support having asurface bearing an improved subbing layer which comprises a mixture ofgelatin and a vinyl polymer in which the ratio of gelatin to polymer andthe dry coverage of the layer are specified.

EP 0583787 A2 discloses the use of glow discharge treatment to enhancethe adhesion of photographic elements. This treatment involves the useof high energy plasma under vacuum which requires specific equipment.

U.S. Pat. No. 5,378,592 discloses the use of a two-layer subbing layer(for photographic materials) wherein the first subbing layer is a layerof polyurethane latex cured with an epoxy compound or adichloro-s-triazine derivative, and the second subbing layer is ahydrophilic colloid layer comprising gelatin.

U.S. Pat. No. 5,532,118 describes the use of a layer of aself-crosslinking polyurethane as an adhesion promoting material forpolyester film support. The polyurethane was not gelatin-grafted nor didthe adhesion promoting layer contain gelatin.

It is desirable to provide polyester film supports having improved wetand dry adhesion of hydrophilic colloid emulsions. It is also desirableto provide such supports that are free of photosensitive activematerials.

U.S. Pat. Nos. 4,855,219, 5,066,572, 5,248,558, 5,330,885, and others,describe gelatin-coated latex polymers and gelatin-grafted latexpolymers and their use in photographic elements. Typically, these latexpolymers are either soft or hard (meth)acrylate copolymer latexes thatare added to protective overcoats for silver halide emulsion layers toimprove resistance to scratch, abrasion, and ferrotyping or are added tointerlayers or silver halide emulsion layers to reduce pressuresensitivity.

SUMMARY OF THE INVENTION

The present invention is an imaging base which includes a polyester filmsupport and an adhesion promoting layer directly adhered to a surface ofthe support. The adhesion promoting layer is formed by the coating andsubsequent drying of a coating composition comprising agelatin-grafted-polyurethane. The gelatin-grafted polyurethane iscovalently bound to the polyurethane through a grafting agent whereinthe ratio of gelatin to polyurethane is from 1:10 to 2:1. In oneembodiment of the invention the imaging support is coated with at leastone silver halide emulsion layer to form a photographic element.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a photographic element having a polyester supportand at least one light-sensitive layer, the support having at least onesurface coated with a gelatin-grafted polyurethane. The gelatin-graftedpolyurethane coating compositions of the invention provide excellentadhesion to the polyester support and to overlying hydrophiliccolloid-containing layers.

In the process of making a photographic element in accordance with thisinvention, the polyurethane adhesive promoting layer may be applied tothe polyester film support either during the preparation of the filmsupport or subsequently thereto. That is, in the preparation ofpolyester film supports, the polymer is melt extruded into a sheet andsubsequently oriented by stretching in both the machine and transversedirections and subsequently treated by several steps including heattreating, heat relaxing, annealing, and the like. This procedure is wellknown in the art and requires no further explanation. The coatingcomposition comprising the gelatin-grafted polyurethane may be appliedat any stage in the known process of preparing polyester photographicfilm base, including before orienting, between the orienting steps, orbefore or after any of the subsequent steps in the preparation of thesupport. The application of the gelatin-grafted polyurethane coatingcomposition is particularly advantageous after completion of theorientation of the polyester support. Compared with the prior art U.S.Pat. Nos. 5,378,592 and 5,532,118 which utilize a polyurethane adhesionpromoting layer with a thin gelatin adhesion promoting layer over thepolyurethane layer the present invention combines the function of thesetwo layers in a single layer, therefore reducing manufacturingcomplexity.

Suitable polyester film supports are polymeric linear polyesters ofbifunctional aromatic dicarboxylic acids and dihydroxy organiccompounds. Generally, they are polyesters derived from terephthalic acidor naphthalene dicarboxylic acids and alkylene glycols. Polyester filmsupports are well known and can be prepared from any of the polyestercompositions described, for example, in Nadeau U.S. Pat. No. 2,943,937or in Alles et al., U.S. Pat. No. 2,627,088. Suitable polyester for useas supports include those prepared from dicarboxylic acids orderivatives thereof, such as terephthalic acid, isophthalic acid,2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid,adipic acid, succinnic acid and mixtures thereof and glycols, such as,ethylene glycol, propylene glycol, butylene glycol, hexamethyleneglycol, cyclohexane diol, 1,4-cyclohexane dimethylol, and mixturesthereof. Especially useful polyester film supports are poly(ethyleneterephthalate) or poly(ethylene naphthalate).

The supports preferably are initially treated with corona discharge(CDT), UV, glow discharge (GDT), flame or other such methods that alterthe support surface. Corona discharge treatment is described in U.S.Pat. No. 4,695,532 and glow discharge treatment is described in U.S.Pat. No. 5,425,980; U.S. Pat. Nos. 3,288,638; 3,837,886; 4,451,497;4,933,267; and EPO application 92/3035562, all of which are incorporatedherein by reference.

The gelatin-grafted polyurethane coating composition is applied to thepolyester film support from an aqueous dispersion using well-knowncoating techniques such as hopper coating, air-knife coating, gravurecoating, roller coating, dip coating, spray coating, wire rod coating,and curtain coating.

The polyurethanes useful in the present invention are water dispersiblepolyurethanes containing carboxylate groups, such as carboxylic acid orcarboxylic acid salt groups, that are covalently bonded to gelatin withthe aid of a grafting agent. Water dispersible polyurethanes are wellknown and are prepared by chain extending a prepolymer containingterminal isocyanate groups with an active hydrogen compound, usually adiamine or diol. The prepolymer is formed by reacting a diol or polyolhaving terminal hydroxyl groups with excess diisocyanate orpolyisocyanate. To permit dispersion in water, the prepolymer isfunctionalized with hydrophilic groups. Anionic, cationic, ornonionically stabilized prepolymers can be prepared.

Anionic dispersions contain usually either carboxylate or sulphonatefunctionalized co-monomers, e.g., suitably hindered dihydroxy carboxylicacids (dimethylol propionic acid) or dihydroxy sulphonic acids. Cationicsystems are prepared by the incorporation of diols containing tertiarynitrogen atoms, which are converted to the quaternary ammonium ion bythe addition of a suitable alkylating agent or acid. Nonionicallystabilized prepolymers can be prepared by the use of diol ordiisocyanate co-monomers bearing pendant polyethylene oxide chains.These result in polynrethanes with stability over a wide range of pH.Nonionic and anionic groups may be combined synergistically to yield"universal" urethane dispersions. For the purpose of the presentinvention, the polyurethane dispersion contains anionic groups that arecarboxylic acid salt groups. The polyurethane dispersion may alsocontain nonionic groups in combination with the carboxylic acid saltanionic groups. In order to provide sufficient carboxylate groups forgrafting it is necessary that the polyurethane has an acid number of atleast 5. Acid number is defined as the milligrams of KOH required toneutralize one gram of polymer.

The polyurethane dispersion useful for the purpose of the presentinvention may be a self-crosslinking polyurethane derived from anisocyanate terminated prepolyrner extended with an aliphatic polyamineand end-capped with N-methylol hydrazide groups such as those describedin U.S. Pat. No. 5,532,118, incorporated herein by reference. For thepurpose of the present invention, it is preferable that the polyurethanebe an aliphatic polyurethane to prevent yellowing upon aging orarchiving of the photographic film.

One of several different techniques may be used to prepare polyurethanedispersions. For example, the prepolymer may be formed, neutralized oralkylated if appropriate, then chain extended in an excess of organicsolvent such as acetone or tetrahydrofuran. The prepolymer solution isthen diluted with water and the solvent removed by distillation. This isknown as the "acetone" process. Alternatively, a low molecular weightprepolymer can be prepared, usually in the presence of a small amount ofsolvent to reduce viscosity, and chain extended with diamine just afterthe prepolymer is dispersed into water. The latter is termed the"prepolymer mixing" process and for economic reasons is much preferredover the former.

Polyols useful for the preparation of polyurethane dispersions includepolyester polyols prepared from a diol (e.g. ethylene glycol, butyleneglycol, neopentyl glycol, hexane diol or mixtures of any of the above)and a dicarboxylic acid or an anhydride (succinic acid, adipic acid,suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalicacid, maleic acid and anhydrides of these acids), polylactones fromlactones such as caprolactone reacted with a diol, polyethers such aspolypropylene glycols, and hydroxyl terminated polyacrylics prepared byaddition polymerization of acrylic esters such as the aforementionedalkyl acrylate or methacrylates with ethylenically unsaturated monomerscontaining functional groups such as carboxyl, hydroxyl, cyano groupsand/or glycidyl groups.

Diisocyanates that can be used are as follows: toluene diisocyanate,tetramethylene diisocyanate, hexamethylene diisocyanate, isophoronediisocyanate, ethylethylene diisocyanate, 2,3-dimethylethylenediisocyanate, 1-methyltrimethylene diisocyanate, 1,3-cycopentylenediisocyanate, 1,4-cyclohexylene diisocyanate, 1,3-phenylenediisocyanate, 4,4'-biphenylene diisocyanate, 1,5-naphthalenediisocyanate, bis-(4-isocyanatocyclohexyl)-methane, 4,4'diisocyanatodiphenyl ether, tetramethyl xylene diisocyanate and thelike.

Compounds that are reactive with the isocyanate groups and have a groupcapable of forming an anion are as follows: dihydroxypropionic acid,dimethylolpropionic acid, dihydroxysuccinic acid and dihydroxybenzoicacid. Other suitable compounds are the polyhydroxy acids which can beprepared by oxidizing monosaccharides, for example gluconic acid,saccharic acid, mucic acid, glucuronic acid and the like. Suitabletertiary amines which are used to neutralize the acid and form ananionic group for water dispersibility are trimethylamine,triethylamine, dimethylaniline, diethylaniline, triphenylamine and thelike.

Diamines suitable for chain extension of the polyurethane includeethylenediamine, diaminopropane, hexamethylene diamine, hydrazine,aminoethylethanolamine and the like.

Solvents which may be employed to aid in formation of the prepolymer andto lower its viscosity and enhance water dispersibility includemethylethylketone, toluene, tetrahydrofuran, acetone, dimethylformamide,N-methylpyrrolidone, and the like. Water-miscible solvents likeN-methylpyrrolidone are much preferred.

The gelatin to be covalently bound to the polyurethane can be any of theknown types of gelatin. These include, for example, alkali-treatedgelatin (cattle bone or hide gelatin), acid-treated gelatin pigskin orbone gelatin), and gelatin derivatives such as partially phthalatedgelatin, acetylated gelatin, and the like, preferably the deionizedgelatins. The gelatin covalently bound to the polyurethane may becrosslinked through the use of a coventional crosslinking agent. Theratio of gelatin to polyurethane is between 1 to 10 and 3 to 1,preferably between 1 to 4 and 3 to 1.

Suitable grafting agents that can be utilized for the attachment ofgelatin to the polyurethane are the carbamoylonium salts, dicationethers, and carbodiimides described in U.S. Pat. No. 5,248,558,incorporated herein by reference. The carbamoylonium compounds useful inthe practice of the present invention can be obtained commercially, orprepared using known procedures and starting materials, such asdescribed in U.S. Pat. No. 4,421,847 and references noted therein,incorporated herein by reference. Representative preferredcarbamoylonium compounds include1-(4-morpholinocarbonyl)-4-(2-sulfoethyl)pyridinium hydroxide, innersalt, and 1-(4-morpholinocarbonyl)pyridinium chloride.

Dication ethers are also useful as grafting agents for bonding gelatinto a polyurethane containing carboxylate groups. Useful dication ethershave the formula: ##STR1##

In this formula, R₁ represents hydrogen, alkyl, aralkyl, aryl, alkenyl,--YR₇, the group ##STR2## with Y representing sulfur or oxygen, and R₇,R₈, R₉, R₁₀, and R₁₁, each independently representing alkyl, alkyl,aralkyl, aryl, or alkenyl. Alternatively, R₈ and R₉, or R₁₀ and R₁₁ maytogether form a ring structure. R₁₀ and R₁₁ may each also representhydrogen. Also, R₁ together with R₂ may form a heterocyclic ring.

R₂ and R₃ each independently represents alkyl, aralkyl, aryl, oralkenyl, or, combined with R₁ or each other, forms a heterocyclic ring.R₄, R₅, and R₆ are independently defined as are R₁, R₂, and R₃,respectively, and can be the same as or different from R₁, R₂, and R₃.

X⁻ represents an anion or an anionic portion of the compound to form anintramolecular (inner) salt. The ethers above can be made by techniquesknown to those skilled in the chemical synthesis art. Useful synthesistechniques include those described in Journal Of American ChemicalSociety, 103, 4839 (1981).

Carbodiimides can also be used to attach gelatin to carboxylatedpolyurethanes. Particularly preferred carbodiimide grafting agents arewater-soluble carbodiimides of the formula:

    R.sub.12 --N═C═N--R.sub.13

wherein each of R₁₂ or R₁₃ is selected form: cycloalkyl having from 5 to6 carbon atoms in the ring: alkyl of from 1 to 12 carbon atoms;monoarylsubstituted lower alkyl radicals, e.g., benzyl-α- andβ-phenylethyl; monoaryl radicals, e.g., phenyl; morpholino; piperidyl;morpholinyl substituted with lower alkyl radicals, e.g.,ethylmorpholinyl; piperidyl substituted with lower alkyl radicals, e.g.,ethylpiperidyl; di-lower alkylamino; pyridyl substituted with loweralkyl radicals, e.g., α, β, γ-methyl-or ethyl-pyridyl; acid additionsalts; and quaternary amines thereof.

For the grafting of gelatin to the polyurethane dispersion, thepolyurethane dispersion is preferably first contacted with the graftingagent and then with gelatin, so that the gelatin preferentially reactswith the polyurethane, instead of gelatin-gelatin cross-linking.Carbamoylpyridinium and dication ether grafting agents areadvantageously utilized in the practice of this invention as these maybe employed to selectively bond to a carboxyl group on a polymerparticle and then with an amino group on the gelatin molecule.Carbamoylpyridinium compounds are particularly preferred.

The contacting of the polyurethane and gelatin is preferably performedin an aqueous medium. The concentration of polyurethane in the aqueousdispersion is preferably less than about 25% and more preferably lessthan about 15% by weight. The concentration of gelatin in the aqueousdispersion is preferably less than about 25% and more preferably lessthan about 15% by weight.

The pH of the aqueous dispersion and the concentration of thepolyurethane and gelatin should be adjusted to prevent bridging ofgelatin molecules between the polyurethane dispersion, or coagulation.The pH of the gelatin is preferably maintained above the isoelectric pHof the gelatin (e.g., above 4.8 and preferably between 8 and 10 forlime-processed bone gelatin). Under such conditions, both thepolyurethane dispersion and the gelatin should have the same charge,preferably negative, in order to minimize coagulation. It is preferredfor this invention that the gelatin-grafted polyurethane dispersion bewashed extensively either by dialysis or diafiltration to remove tracesof reaction byproducts and low molecular weight species.

The gelatin-grafted polyurethane dispersions of the invention can beused in coating compositions alone or in combination with otherwater-dispersible or water soluble polymers, including; latex polymersprepared from ethylenically unsaturated monomers such as (meth)acrylicacid, (meth)acrylic acid esters, styrene and its derivatives, vinylhalides, itaconic acid and its mono- and di-esters, maleic acid and itsmono- and di-esters, (meth)acrylonitrile, (meth)acrylamides, olefins,and others; water dispersible polyurethanes and polyesters; hydrophiliccolloids such as gelatin, dextran, gum arabic, zein, cassein, pectin,agar--agar, polyvinyl alcohol, poly(vinyl pyrrolidone), and the like.Preferably, the gelatin-grafted polyurethane dispersions of theinvention comprise from about 50 to 100 weight % of the dried adhesionpromoting layer.

Coatings containing the gelatin-grafted polyurethane dispersions mayadditionally include; crosslinking agents such as aziridines,carbodiimides, epoxides, triazines, polyisocyanates, and methoxyalkylmelamines; gelatin hardeners such as those described, for example, inResearch Disclosure No. 38957, September 1996, pages 599 to 600;surfactants and coating aids; rheology modifiers; and inorganic orpolymeric matting agents.

The total dried coating weight for the adhesion promoting layer of theinvention is from about 10 to about 5000 mg/m², preferably from about 50to 500 mg/m².

The photographic elements of this invention are photographic films inwhich the image-forming layer is a radiation-sensitive silver halideemulsion layer. Such emulsion layers typically comprise a film-forminghydrophilic colloid. The most commonly used of these is gelatin andgelatin is a particularly preferred material for use in this invention.Useful gelatins include alkali-treated gelatin (cattle bone or hidegelatin), acid-treated gelatin (pigskin gelatin) and gelatin derivativessuch as acetylated gelatin, phthalated gelatin and the like. Otherhydrophilic colloids that can be utilized alone or in combination withgelatin include dextran, gum arabic, zein, casein, pectin, collagenderivatives, collodion, agar--agar, arrowroot, albumin, and the like.Still other useful hydrophilic colloids are water-soluble polyvinylcompounds such as polyvinyl alcohol, polyacrylamide,poly(vinylpyrrolidone), and the like.

The photographic elements of the present invention can be simpleblack-and-white or monochrome elements comprising a support bearing alayer of light-sensitive silver halide emulsion or they can bemultilayer and/or multicolor elements.

Color photographic elements of this invention typically contain dyeimage-forming units sensitive to each of the three primary regions ofthe spectrum. Each unit can be comprised of a single silver halideemulsion layer or of multiple emulsion layers sensitive to a givenregion of the spectrum. The layers of the element, including the layersof the image-forming units, can be arranged in various orders as is wellknown in the art.

A preferred photographic element according to this invention comprises asupport bearing at least one blue-sensitive silver halide emulsion layerhaving associated therewith a yellow image dye-providing material, atleast one green-sensitive silver halide emulsion layer having associatedtherewith a magenta image dye-providing material and at least onered-sensitive silver halide emulsion layer having associated therewith acyan image dye-providing material.

In addition to emulsion layers, the elements of the present inventioncan contain auxiliary layers conventional in photographic elements, suchas overcoat layers, spacer layers, antistatic layers, magnetic recordinglayers, filter layers, interlayers, antihalation layers, pH loweringlayers (sometimes referred to as acid layers and neutralizing layers),timing layers, opaque reflecting layers, opaque light-absorbing layersand the like. The support can be any suitable support used withphotographic elements. Typical supports include polymeric films, paper(including polymer-coated paper), glass and the like. Details regardingsupports and other layers of the photographic elements of this inventionare contained in Research Disclosure, Item 36544, September, 1994.

The light-sensitive silver halide emulsions employed in the photographicelements of this invention can include coarse, regular or fine grainsilver halide crystals or mixtures thereof and can be comprised of suchsilver halides as silver chloride, silver bromide, silver bromoiodide,silver chlorobromide, silver chloroiodide, silver chorobromoiodide, andmixtures thereof. The emulsions can be, for example, tabular grainlight-sensitive silver halide emulsions. The emulsions can benegative-working or direct positive emulsions. They can form latentimages predominantly on the surface of the silver halide grains or inthe interior of the silver halide grains. They can be chemically andspectrally sensitized in accordance with usual practices. The emulsionstypically will be gelatin emulsions although other hydrophilic colloidscan be used in accordance with usual practice. Details regarding thesilver halide emulsions are contained in Research Disclosure, Item36544, September, 1994, and the references listed therein.

The photographic silver halide emulsions utilized in this invention cancontain other addenda conventional in the photographic art. Usefuladdenda are described, for example, in Research Disclosure, Item 36544,September, 1994. Useful addenda include spectral sensitizing dyes,desensitizers, antifoggants, masking couplers, DIR couplers, DIRcompounds, antistain agents, image dye stabilizers, absorbing materialssuch as filter dyes and UV absorbers, light-scattering materials,coating aids, plasticizers and lubricants, and the like.

Depending upon the dye-image-providing material employed in thephotographic element, it can be incorporated in the silver halideemulsion layer or in a separate layer associated with the emulsionlayer. The dye-image-providing material can be any of a number known inthe art, such as dye-forming couplers, bleachable dyes, dye developersand redox dye-releasers, and the particular one employed will depend onthe nature of the element, and the type of image desired.

Dye-image-providing materials employed with conventional color materialsdesigned for processing with separate solutions are preferablydye-forming couplers; i.e., compounds which couple with oxidizeddeveloping agent to form a dye. Preferred couplers which form cyan dyeimages are phenols and naphthols. Preferred couplers which form magentadye images are pyrazolones and pyrazolotriazoles. Preferred couplerswhich form yellow dye images are benzoylacetanilides andpivalylacetanilides.

The photographic processing steps to which the raw film may be subjectmay include, but are not limited to the following:

1) color developing→bleach-fixing→washing/stabilizing;

2) color developing→bleaching→fixing→washing/stabilizing;

3) color developing→bleaching→bleach-fixing→washing/stabilizing;

4) colordeveloping→stopping→washing→bleaching→washing.fwdarw.fixing→washing/stabilizing;

5) color developing→bleach-fixing→fixing→washing/stabilizing;

6) color developing→bleaching→bleach-fixing→fixing→washing/stabilizing;

Among the processing steps indicated above, the steps 1), 2), 3), and 4)are preferably applied. Additionally, each of the steps indicated can beused with multistage applications as described in Hahm, U.S. Pat. No.4,719,173, with co-current, counter-current, and contraco arrangementsfor replenishment and operation of the multistage processor.

Any photographic processor known to the art can be used to process thephotosensitive materials described herein. For instance, large volumeprocessors, and so-called minilab and microlab processors may be used.Particularly advantageous would be the use of Low Volume Thin Tankprocessors as described in the following references: WO 92/10790; WO92/17819; WO 93/04404; WO 92/17370; WO 91/19226; WO 91/12567; WO92/07302; WO 93/00612; WO 92/07301; WO 02/09932; U.S. Pat. No.5,294,956; EP 559,027; U.S. Pat. No. 5,179,404; EP 559,025; U.S. Pat.No. 5,270,762; EP 559,026; U.S. Pat. No. 5,313,243; U.S. Pat. No.339,131.

The present invention is also directed to photographic systems where theprocessed element may be re-introduced into the cassette. These systemallows for compact and clean storage of the processed element until suchtime when it may be removed for additional prints or to interface withdisplay equipment. Storage in the roll is preferred to facilitatelocation of the desired exposed frame and to minimize contact with thenegative. U.S. Pat. No. 5,173,739 discloses a cassette designed tothrust the photographic element from the cassette, eliminating the needto contact the film with mechanical or manual means. Published EuropeanPatent Application 0 476 535 A1 describes how the developed film may bestored in such a cassette.

The present invention will now be described in detail with reference toexamples; however, the invention should not be limited to theseexamples.

EXAMPLES Preparation of Gelatin-Grafted Polyurethane Dispersion

Gelatin-grafted polyurethane P-1: A commercially available,water-dispersible polyurethane (Witcobond 236, a product of Witco Corp.)was grafted to gelatin at a weight ratio of 60 parts polyurethane to 40parts gelatin by the following procedure: 213 g of polyurethanedispersion (20% solids) and 200 g distilled water were introduced to a 2liter round-bottom 3-necked flask equipped with a condenser and overheadstirrer. The flask was immersed in a constant temperature bath at 60° C.1.1 g of 1-(4-morpholinocarbonyl)-4-(2-sulfoethyl)pyridinium hydroxide,inner salt was dissolved in 75 g of water and added to the dilutedpolyurethane dispersion. Reaction was continued for 40 minutes, duringwhich time 27.8 g of gelatin was dissolved in 250 g of water withheating at 60° C. and neutralized to pH 9 with triethylamine. Thegelatin solution was then added via dropping funnel and the graftingreaction allowed to proceed for another 30 minutes. After cooling to 40°C. the product was filtered, with very little insoluble matter observed,then refrigerated. The gelatin-grafted polyurethane dispersion soobtained was stable to storage for months.

Gelatin-grafted polyurethanes P-2 and P-3: Additional gelatin-graftedpolyurethanes were prepared in a manner analogous to that used toprepare P-1. For P-2 and P-3, Witcobond 236 was used as the polyurethanedispersion that was grafted to gelatin at a weight ratio of 75 partspolyurethane to 25 parts gelatin for P-2, and 25 parts polyurethane to75 parts gelatin for P-3.

The above gelatin-grafted polyurethane dispersions were used in thefollowing example coating compositions.

Testing:

Adhesion for the coatings was tested by placing the samples in filmdeveloper at 35° C. for 1 minute. While still wet, a one millimeter wideline was scribed in the coating and a hard rubber pad was rubbed acrossthe scribe line. The change in the width of the scribe line was used asa measure of the adhesion (i.e., excellent adhesion in this test meansno observable change in the width of the scribe line). Samples wereincubated for 24 hours at 30° C. and 50% RH prior to adhesion testing.

Examples 1 to 3 and Comparative Samples A to C

The following examples demonstrate the utility of the gelatin-graftedpolyurethanes of the invention as an adhesion promoting layer. Thefollowing compositions were applied onto a corona discharge treated,biaxially oriented polyethylene terephthalate film support and dried at130° C. for 2 minutes to give a layer with a dried coating weight of 100mg/m².

Example 1

Polymer P-1 0.7 wt %

Triton X-100 Surfactant (Rohm & Haas) 0.06 wt %

CX100 polyfunctional aziridine (Zeneca 0.035 wt %

Resins)

water balance

Example 2

Polymer P-2 0.7 wt %

Triton X-100 Surfactant (Rohm & Haas) 0.06 wt %

CX100 polyfunctional aziridine (Zeneca 0.035 wt %

Resins)

water balance

Example 3

Polymer P-3 0.7 wt %

Triton X-100 Surfactant (Rohm & Haas) 0.06 wt %

CX100 polyfunctional aziridine (Zeneca 0.035 wt %

Resins)

water balance

These coatings gave excellent adhesion to the energy-treated filmsupport. These layers were also overcoated with a 5000 mg/m² gelatinlayer to simulate overcoating the adhesion promoting layer with ahydrophilic silver halide emulsion layer or curl control layer. Aftercoating, the thick gelatin layer was chill-set at 5° C. and first driedat 21° C. and then at 38° C. This gelatin overcoat layer also containedabout 1 wt % of a bis(vinylsulfonylmethyl)ether gelatin-hardening agent.These examples gave good to excellent adhesion of the gelatin overcoatto the film support.

For comparison purposes, the following coatings were applied and testedfor adhesion. Comparative Sample A, which is a poly(methylacrylate-co-vinylidene chloride-co-itaconic acid) terpolymer latex thatis well known in the photographic art as a priming layer forphotographic film support and described in U.S. Pat. No. 3,143,421, wasapplied onto a corona discharge treated, biaxially oriented polyethyleneterephthalate film support and dried at 130° C. for two minutes.

Comparative Sample B comprised the above mentioned terpolymer latex with40 weight % gelatin added to the coating. The coating was prepared in ananalogous manner to that described above for Sample A.

Comparative Sample C comprised Witcobond 236 polyurethane with 40 weight% gelatin added to the coating. In this sample, the gelatin was notgrafted to the polyurethane. The coating was as made as described above.The coatings of Samples A, B, and C were then overcoated with the thickgelatin layer described above and tested for adhesion. ComparativeSamples A and B gave very poor adhesion results with almost completeremoval of the thick gelatin layer from the film support. ComparativeSample C gave only fair adhesion.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

What is claimed is:
 1. An imaging base comprising:a polyester filmsupport; an adhesion promoting layer directly adhered to a surface ofsaid support formed by the coating and subsequent drying of a coatingcomposition comprising gelatin-grafted polyurethane comprising gelatincovalently bound to a polyurethane through a grafting agent, wherein aratio of gelatin to polyurethane is from 1:10 to 2:1.
 2. The imagingbase of claim 1, wherein said grafting agent comprises carbamoyloniumsalts, dication ethers or carbodiimides.
 3. The imaging base of claim 1,wherein said coating composition further comprises another polymerselected from the group consisting of water soluble polymers or waterdispersible polymers.
 4. The imaging base of claim 1, wherein thecoating composition further comprises crosslinking agents, conductiveagents, fillers, magnetic recording particles, dyes, pigments, coatingaids, surfactants, rheology modifiers, lubricating agents or mattingagents.
 5. The imaging base of claim 1 wherein said support comprisespoly(ethylene terephthalate) or poly(ethylene naphthalate).
 6. Aphotographic element comprising:a polyester film support; an adhesionpromoting layer directly adhered to a surface of said support formed bythe coating and subsequent drying of a coating composition comprisinggelatin-grafted polyurethane comprising gelatin covalently bound to apolyurethane through a grafting agent, wherein a ratio of gelatin topolyurethane is from 1:10 to 2:1. at least one silver halide emulsionlayer superposed on said support.
 7. The photographic element of claim6, wherein said grafting agent comprises carbamoylonium salts, dicationethers or carbodiimides.
 8. The photographic element of claim 6, whereinsaid coating composition further comprises another polymer selected fromthe group consisting of water soluble polymers or water dispersiblepolymers.
 9. The photographic element of claim 6, wherein the coatingcomposition further comprises crosslinking agents, conductive agents,fillers, magnetic recording particles, dyes, pigments, coating aids,surfactants, rheology modifiers, lubricating agents or matting agents.10. The photographic element of claim 6 wherein said support comprisespoly(ethylene terephthalate) or poly(ethylene naphthalate).